The present invention relates generally to use of recombinant viruses as vectors, and more specifically to recombinant bovine immunodeficiency virus (BIV) based vector constructs capable of expressing a desired protein in target cells.
The use of recombinant virus vectors in a variety of applications including, for example, gene therapy requires that the virus not be capable of replication in the target cells to avoid the possibility of uncontrolled virus or cell proliferation. In addition to safety, the recombinant virus vector system must be efficient and accurate.
Retroviruses have been used as vectors to mediate gene transfer into eukaryotic cells. Retroviruses are RNA viruses that include the subfamilies lentivirus, spumavirus, and oncovirus. These viruses can replicate and integrate into a host cell genome through a DNA intermediate, generally called a provirus.
The viral vectors are generally constructed such that the majority of the viral genes are deleted and replaced by a gene of interest. Most frequently the gene of interest is transcribed under the control of the viral regulatory sequences within the long terminal repeat (LTR). Altematively, the gene of interest may be expressed under the regulation of its own internal promoter. The genes which have been deleted from the vector are generally provided by one or more helper or packaging constructs in a packaging cell line (Bender et al., J. Virol. 61: 1639–1649 (1987) and Miller et al., Biotechniques, 7:980–990 (1989)). Also see Markowitz et al., J. Virol. 62:1120–1124 (1988) wherein complementary portions of the helper construct were divided on two separate constructs. The packaging cell line may be transfected with the retroviral vector, thereby producing vector RNA that is packaged into the virus particles. These released virus particles are replication defective and can be used to deliver the retroviral vector carrying a heterologous gene of interest to target cells.
To increase safety, efficiency and accuracy of the recombinant vector systems, various improved recombinant systems have been constructed. One type of improvement includes making safer packaging cell lines that are generated by deletions in the 3′ Long Terminal Repeat (LTR). Other improvements include increasing the host range by replacement of one viral env gene with that of another viral env gene, thereby creating a hybrid producer line that generates pseudotyped helper viruses. More specifically, HIV has been given an extended host cell range by pseudotyping with the unrelated viruses VSV and HSV (Zhu et al., J. AIDS, 3:215–219 (1990) and Naldini et al., Science, 272:263–267, (1996)). Further improvements have been made by the use of minimum viral coding regions in the vector. Additionally, most packaging cell lines currently in use have been transfected with separate plasmids, each containing one of the necessary coding sequences so that multiple recombination events are necessary before replication competent virus can be produced.
In contrast to vectors derived from oncoviruses, lentivirus can infect nondividing cells. This property is especially useful for in vivo gene therapy.
BIV generally does not infect human cells and, therefore, the use of a BIV genomic backbone in the vectors of the present invention overcomes difficulties of prior packaging cell lines and further provides other related advantages for improved vector construction.